<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        span{
            color: pink;
        }
    </style>

    <link href="../css/demo.css" rel="stylesheet">
</head>
<body>
    <!--1.内联-->
    <div style="color: red">Hello css</div>
    <!--2.内部-->
    <span>Hello World</span>
    <!--3.外部-->
    <p>Hello zhangsan</p>
</body>
</html>